U.S. Pat. Nos. 3,896,131 and 3,985,882 describe substituted 6,7-dihydro-5-methyl-1-oxo-1H,5H-benzo[ij]quinolizine-2-carboxylic acids which are useful antimicrobial agents. Those patents describe compounds which may be substituted in the 8, 9 or 10 position by a number of substituents including amio (--NH.sub.2), N,N-dialkylamino [(CH.sub.3).sub.2 N--], lower alkanamido and trifluoroacetamido groups. The present invention relates to compounds containing more complex nitrogen-containing substituents than those described in the aforementioned patents and specifically in the 8-position. It also relates to novel compounds which start with a non-aromatic aminomethyl group (NH.sub.2 CH.sub.2 --) in the 8-position and provide further derivatives.